Metallic foil and method of manufacture



Patented May 15, 1934 METALLIC FOIL AND METHOD OF MANUFACTURE UrlynClifton Tainton,

St. Louis, and Frank W.

Harris, Clayton, Mo'.; said Harris assignor to said Tainton No Drawing.

Application April 20, 1931,

Serial No. 531,610

8 Claims.

This invention relates to metallic foil, and with regard to certain morespecific features, to improved methods of producing metallic foil havingsmooth bright surfaces.

Among the several objects of the invention may be noted the provision ofmetal for manufacturing foil "which may be processed to secure foilhaving a desirable; bright surface; and the provision of a process foreconomically manufactur- 10 ing thin metal foil having a, smooth brightsurface. Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the elements and combinations ofelements, steps and sequence of steps and features of synthesis whichwill be exemplified in the description hereinafter and the scope of theapplication of which will be indicated in the following claims.

Metal foil is manufactured from the less precious metals by subjecting astrip of metal to repeated rolling operations until the thickness isreduced to the desired degree. The unit cost of this rolling operationis greatly reduced by a procedure known as pack-rolling, comprising 5placing a number of strips of metal together and passing themsimultaneously through rolls. This latter method, however, isobjectionable in that the foil produced thereby, except for the twooutside surfaces of the outer pieces in contact with the rolls, has amatte or eggshell surface instead of the smooth bright surface which isdesired. It hasnot been possible hitherto to produce a smooth brightsurface on foil except by actual contact with a polished roll. This fact5 has operated to the advantage of metals such as lead and tin which onaccount of their softness can be readily rolled at high speeds andeasily take a bright finish from the rolled surface. It has operated tothe disadvantage of. other metals, and in particular of zinc. Althoughintrinsically cheaper than lead'and tin per unit of foil produced, bypresent methods zinc cannot be given a bright surface except by arelatively expensive operation of individual piece rolling with polisheda crystalline or non-homogeneous structure and do not resist deformationof the surface equally at all points. Accordingly when two metalsurfaces are pressed together under exterior force, the harder parts ofone metal project into the softer parts of the other and thus produce arough or dull, eggshell or matte surface on each.

Although this dull effect has been thought to be characteristic of allmetals, we have discovered that in the case of zinc it can be prevented.Zinc possesses to a high degree a property which may be termedplasticity or ductility, that is to say, Zinc has characteristics suchthat even when cold it will yield or fiow gradually under appliedstress. This property is undesirable for most structural purposes andconsiderable work has been done in the direction of alloying zinc withother metals in order to overcome this plasticity. A common example of azinc alloy in which the plasticity or ductility has purposely beendestroyed is die casting metal, which normally consists of 93% of zincand 1% of copper, aluminumand magnesium. This die casting alloy is hardand strong and does not flow under stress. Other alloys have beendeveloped to improve the qualities of zinc as a structural material forroofing sheets, piping, etc.

For the purposes of this invention, however, it is desirable that theplastic or ductile properties of the zinc metal be retained. It is alsodesirable to restrain or prevent the recrystallization which occurs inpure zinc even at ordinary or room temperatures, which itself occasionsa matte surface when zinc sheets are rolled in a pack.

We have discovered that certain substances if added to the zinc inproper amount will inhibit this recrystallization property while notsubstantially decreasing, and in some cases actually increasing, theplastic or ductile properties of the metal. It is important that theadded substances be not present in such amounts as to produce a hardstrong metal, which while useful for ordinarypurposes, would be oflittle utility for the purposes herein considered. For example, anysubstantial amounts of iron, cadmium or magnesium would be detrimentalto the purposes of this invention.

Our researches have shown that the desired effect may be produced by theaddition to pure zinc of various elements in carefully graduatedamounts. In the case of metals which form a brittle eutectic alloy withzinc, the amount of alloying metal added should be less than is requiredto form the eutectic. If aluminum be used, for example, the amount addedshould be less than 5.0%, this representing the corresponding eutecticmixtures. The following metals have been tried and found efiective forour purposes:

Antimony in amounts up to 4%.

Copper and aluminum in amounts up to 2%.

Tin and silver in amounts up to 1%.

Mercury in amounts up to .1%. v

Various combinations of these metals have proved effective and it isprobable that other metals may also be used. On account of the largenumber of the elements, it is not possible to cover in thisspecification all of the combinations of zinc with other metals that maybe efiective. Accordingly we do not wish to limit ourselves to themetals specified but may use any substances which when added to zincmetal will restrain or even totally inhibit the recrystallization of themetal, which normally occurs at ordinary temperatures, and at the sametime will not substantially diminish the plasticity or ductility of themetal.

It is not necessary for the purpose of this invention that the addedsubstances be metals.

We have also found that pure zinc electrolytically deposited from asolution containing colloids occludes sumcient of the colloid to preventrecrystallization of the .zinc and thus may be used according to thisspecification with the production of bright foil surfaces throughout thepack.

As an illustration of the method of carrying this invention into effectwe will describethe production of bright foil from cathode zinc and alsofrom an alloy, In the former case, according to our preferred method,zinc is deposited from a sulphate solution containing about 250 gramsper liter of sulphuric acid and about 60 grams per liter of zinc at acathodic current density of about 100 amperes per square foot. To theelectrolyte is added a colloid such as silicic acid or gum arabic inamounts representing about one to four pounds per ton of zinc deposited.

The zinc may be deposited upon a starting sheet of aluminum from whichit may bereadily detached when it has reached the required thickness.Alternatively, the zinc deposit may be built upon a thin starting sheetof zinc which when completed can be rolled without separation of thedeposit from the starting sheet. In the production of continuous stripsof foil a drumshaped aluminum cathode surface may be employed, thisbeing rotated at the appropriate speed according to known methods sothat a continuous strip of cathode zinc is produced which after washingwith water may be passed directly to the rolls. After a zinc cathode hasbeen given a preliminary rolling operation, several sheets aresuperimposed and passed through the rolls as a pack. We havesuccessfully rolled as many as thirty-two sheets at a time in this way.Preferably, the roll should be con ducted at ordinary temperatures, asincreasing temperature tends to promote recrystallization of the zinc.It is also of advantage to separate the sheets occasionally during therolling operation, though not necessarily after each passage through therolls.

It will be found that foil made in this way can be rolled to a thicknessof .0003 inch or less, which represents a yield of about 13,500 squareinches per pound of zinc. All of the foil so produced will be found tohave a bright surface even though it may have been reduced toone-hunamount of other metal is introduced. In a typical case forexample we add to one ton of molten zinc say three pounds of copper andone pound of antimony. The metal is thoroughly mixed and then pouredinto a mold to form a slab, for example, two inches thick and ofdimensions ,appropriate to the length and width of strip desired. Thefirst rolling is carried out at an.elevated temperature, say 250 C. Whenthe thickness has been suitably reduced, say to one-thirtysecond of aninch, the strip is cooled down and then pack-rolled as described abovein the case of the cathode deposited zinc. This procedure also will befound to result in a foil with a brilliant, shining surface althoughthis surface is not derived from contact with the rolls themselves.

Summarizing the foregoing, it will be seen that our invention offers thefollowing advantages:

1. A much greater area of foil can be obtained from a given weight ofthe modified zinc herein described than from the lead-tin combinationnormally used. On account of the relatively low cost of zinc thispermits a great saving in cost.

2. The foil produced is of exceptionally good quality and pleasing inappearance; The surface retains its brightness when exposed tooxidation, dirt, fingermarks, etc., much longer than in the case of foilhaving a dull surface. Moreover. the zinc foil-is considerably strongerand tougher than the lead-tin foil which is now ordinarily used and willtherefore withstand more handling and bending without breakage.

3. On account of the fact that a large number of strips can be rolledsimultaneously, the production capacity of a set of rolls is muchgreater than when rolling single or double sheets, and rolling costs arecorrespondingly reduced.

In view of the foregoing, it will be seen that the several objects ofthe invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above compositions andprocedures with- 125 out departing from the scope of the invention, itis intended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

We claim:

1. The process of producing metallic foil having a smooth bright surfacefrom zinc, said process comprising alloying at least one second metalwith said zinc, said second metal being of a character and suificient inamount to restrain said zinc from re-crystallization at ordinarytemperatures when worked cold by compressive operations but only in suchamount as will leave the resulting metal produce ductile and workablecold by compressive operations, and then simultaneously cold rolling anumber of sheets formed from said alloy superimposed upon one another.

2. The process of producing metallic foil having a smooth bright surfacefrom zinc, said process comprising alloying copper and antimony, withsaid zinc as the basic material, in percentages to inhibitrecrystallization when the resulting zinc alloy is worked cold bycompressive operations, said copper and antimony being employed in suchamounts that while re- 150 straining or inhibiting there-crystallization of said zinc at ordinary temperatures they are notemployed in suflicient amount to'destroy the ductility and cold workablecharacteristics of the basic zinc material, and then simultaneously coldrolling in superposed relationship a number of sheets formed from saidalloy.' I

3. The process of producing a metallic foil having a smooth brightsurface from substantially pure zinc, said process comprisingelectrolytically depositing said zinc from a solution,

having therein a colloid said colloid inhibitingre-crystallization ofsaid zinc at ordinary temperatures but of a character to leave theresultre-crystallization of said zinc at ordinary temperatures butleaving the zinc productwith relatively ductile characteristics thatlend to cold working by successive compressive operations,

and simultaneously cold rolling when superposedone upon another a numberof sheets formed from said electrolytically deposited zinc to form saidmetallic foil. I

' 5. A "rolled metallic foil having a smooth bright surface and composedof zinc containing a substance capable of restraining or inhibiting therecrystallization characteristic of pure zinc at ordinary temperatures.

6. A rolled metal foil as per claim 5, in which an occluded colloid isrelied' upon to provide a material whereby the recrystallizationcharacteristic is inhibited. v

'7. A rolled metal foil as per claim 5, in which at least one secondmetal is relied upon for preventing the recrystallization characteristicof 'zinc during the rolling process.

8. A rolled metal foil as per claim 5, in which at least one secondmetaL'as copper or antimony, is relied upon for restraining therecrystallization characteristic of zinc during the period while therolling into the form of a foil is taking place.

URLYN CLIFTON 'TAINTON. FRANK w. HARRIS.

